Additive manufacturing methods for forming high-temperature composite structures and related structures

ABSTRACT

Methods for fabricating high-temperature composite structures (e.g., structures comprising carbon-carbon composite materials or ceramic composite matrix (CMC) materials and configured for use at temperature at or exceeding about 2000° F. (1093° C.)) include forming precursor structures by additive manufacturing (“AM”) (e.g., “3D printing). The precursor structures are exposed to high temperatures to pyrolyze a precursor matric material of the initial 3D printed structure. A liquid resin is used to impregnate the pyrolyzed structure, to densify the structure into a near-net final shape. Use of expensive and time-consuming molds and post-processing machining may be avoided. Large, unitary, integrally formed parts conducive for use in high-temperature environments may be formed using the methods of the disclosure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject matter of this application is related to the subject matterof U.S. patent application Ser. Nos. 16/380,066; 16/380,131; 16/380,208;16/380,272; 16/380,328; 16/380,390, all filed Apr. 10, 2019, and thedisclosure of each of which is hereby incorporated herein in itsentirety by this reference.

TECHNICAL FIELD

Embodiments of the disclosure relate to methods for formingthree-dimensional (3D) integrated composite structures and to relatedstructures and, more particularly, to methods for forminghigh-temperature carbon-carbon (C/C) structures or ceramic matrixcomposite (CMC) structures by multi-axis additive manufacturing withsubsequent densification using a liquid resin, and to relatedstructures.

BACKGROUND

High-temperature structures, particularly those to be used in theaerospace industry, are conventionally fabricated from compositematerials (e.g., reinforced materials), such as carbon-fiber-reinforcedcarbon matrix materials (e.g., carbon-carbon composite (C/C) materials)or fiber-reinforced (e.g., carbon-fiber-reinforced,glass-fiber-reinforced, quartz-fiber-reinforced,ceramic-fiber-reinforced, other-fiber-reinforced) ceramic matrixcomposite (CMC) materials. These “composite materials” include a matrixphase (e.g., carbon matrix, ceramic matrix) in which a reinforcing fiberphase is embedded. To form conventional composite material structures,conventional fabrication techniques generally use time-consuming andcostly processes in which intricate continuous-fiber multi-axialtextiles are woven (e.g., into a “dry preform”) and infused withpolymeric materials to form a composite substance (e.g., “block”) thatis placed in or on molds prior to heating (e.g., curing (e.g., autoclavecuring)) to form a machinable block. Alternatively, continuous fiberreinforced polymer precursor materials (i.e., “prepreg” materials) areassembled (e.g., “laid up”)—often by hand—in multiple layers (e.g., intoa “wet preform”) in or on molds prior to heating (e.g., curing (e.g.,autoclave curing)) to convert the “laid up” precursor structures intofinal, rigid structures. These processes tend to be labor intensive(e.g., often requiring highly-trained technicians), be expensive (e.g.,including the cost of fabricating the molds), require a long lead time(e.g., to allow time to fabricate the molds before the fabrication ofthe dry preforms or before the laying-up of prepreg materials into thewet preforms), and require expensive tooling.

Adding to the cost, timing, and complexity of conventional fabricationmethods, forming structures by such processes also often involvesforming several smaller parts and then assembling them together (e.g.,with seals, joints), to form a final, assembled, larger component of adevice or system. Great time and care is required to ensure thatfabricated structures are free from unwanted gaps that could be pointsof failure during use of the assembled parts.

Moreover, the composite material structures formed by conventionalcomposite-material-fabrication techniques are generallyessentially-solid blocks, or thick-walled billets, of material that arethen machined and shaped into a final, desired shape. These end-processmachining and shaping steps, and the tooling needed for such steps, alsoadd to the time and cost of the fabrication process and, if notperformed precisely, may introduce defects into the final structure.

Accordingly, fabricating high-temperature composite structures continuesto present challenges.

BRIEF SUMMARY

In some embodiments, a method—for forming a high-temperature compositestructure—comprises forming a 3D precursor structure. Forming the 3Dprecursor structure comprises depositing, along a direction, an amountof a filament material. The filament material comprises a precursormatrix material having embedded therein a fiber material. An additionalamount of the filament material is deposited on the amount of thefilament material. The 3D precursor structure is pyrolyzed to form apyrolyzed intermediate structure. The pyrolyzed intermediate structureis impregnated with a liquid resin to form an impregnated structure. Theimpregnated structure is exposed to a high-temperature environment tosolidify material from the liquid resin within pores of the pyrolyzedintermediate structure.

In some embodiments, a method—for forming a compositestructure—comprises heating a precursor structure comprising a precursormatrix material embedded with a reinforcing material to solidify atleast some of the precursor matrix material and form an intermediatestructure. The intermediate structure is impregnated with a liquid resinto add carbon or ceramic material to the intermediate structure and forma densified structure. The densified structure is heated at atemperature between about 932° F. (500° C.) and about 5432° F. (3000°C.).

Moreover, in some embodiments, a method—of forming a high-temperaturecarbon-carbon or ceramic matrix composite sandwich structure—comprisesoperating a robotic 3D printing machine to lay, along an axis, aprecursor matrix material comprising a fiber embedded therein and form a3D precursor structure defining at least one void between planarportions. The 3D precursor structure is pyrolyzed at a temperatureexceeding about 932° F. (500° C.) to form a porous intermediatestructure. A liquid resin—comprising carbon or a preceramic material—isintroduced into pores of the porous intermediate structure to form animpregnated intermediate structure. The impregnated intermediatestructure is exposed to a temperature exceeding about 932° F. (500° C.).

Also disclosed is a composite structure, formed by pyrolyzing anddensifying a 3D printed precursor structure of a precursor matrixmaterial embedded with a reinforcing phase. The composite structurecomprises an intermediate portion, defining a series of cells, betweenan upper portion and a lower portion. The intermediate portion, theupper portion, and the lower portion each comprise a composite materialcomprising the reinforcing phase embedded within a matrix phase formedfrom the precursor matrix material. The intermediate portion, the upperportion, and the lower portion are integral with one another.

Moreover, disclosed is a high-temperature composite structure comprisinga pyrolyzed structure comprising a matrix phase having an embeddedreinforcing phase. The pyrolyzed structure defines a sandwich structure.The high-temperature composite structure also comprises solid carbon orceramic material filling pores of the pyrolyzed structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a 3D printing machine, including a robotand an end-effector positioned relative to a part being fabricated on abuild plate, which 3D printing machine may be utilized according toembodiments of the disclosure.

FIG. 2 is an isometric view of a continuous fiber extruder module thatmay be used in the end-effector shown in FIG. 1.

FIG. 3 is an isometric view of a nozzle assembly in the extruder moduleshown in FIG. 2.

FIG. 4 is a cross-sectional view of the nozzle assembly shown in FIG. 3relative to a build-plate.

FIG. 5 is a top view of a part being fabricated by, for example, the 3Dprinting machine shown in FIG. 1, and showing filaments being depositednon-sequentially.

FIG. 6 is a side view of a part being fabricated by, for example, the 3Dprinting machine shown in FIG. 1, and showing alternating continuousfiber filament layers and polymer filament layers.

FIG. 7 is a side view of a support structure on which a part will befabricated by, for example, the 3D printing machine shown in FIG. 1, andshowing a support structure deposition nozzle

FIG. 8 is a side view of the support structure shown in FIG. 7, andshowing a filament deposition nozzle smoothing a top surface of thesupport structure.

FIG. 9 charts embodiments of methods for fabricating high-temperaturecomposite (e.g., carbon-carbon, ceramic matrix composite) structures,according to the present disclosure.

FIG. 10 is a perspective, schematic illustration of a high-temperaturecomposite structure, having a sandwich structure form, formableaccording to embodiments of the present disclosure.

DETAILED DESCRIPTION

Disclosed are methods of fabricating high-temperature compositestructures using additive manufacturing techniques. Additivemanufacturing (“AM”) is a technology and technique used for what iscommonly referred to in the art as “3D printing.”

One type of conventional AM is fused filament fabrication (“FFF”), an AMtechnique in which a stock material is fed to a heated nozzle, fromwhich the stock material is extruded to be laid down, layer by layer, tobuild up a desired product. The stock material may a polymer (e.g., amolten polymer) or a fiber-reinforced polymer material provided in theform of, e.g., pre-shaped filaments or pellets. Upon being extruded fromthe nozzle, the molten stock material immediately begins to harden. Suchconventional “3D” printing systems may not be conducive for use informing structures that are to be used at high temperatures (e.g., attemperatures about or exceeding 2000° F. (1093° C.)). This is becausepolymeric materials used in conventional FFF melt well below 1000° F.(538° C.) and would, thus, provide no structural capability at hightemperatures. Metallic materials, on the other hand, may be capable ofwithstanding high temperatures, but using these materials in 3D printingprocesses may yield structures with intrinsically lower specificstrengths than carbon-carbon or CMC structures. Such 3D printedmetal-based structures may also be susceptible to degradation (e.g.,oxidation) in high-temperature applications and/or may becomestructurally unsound at high temperatures. Some embodiments of thepresent disclosure, however, may be tailored for forming compositematerial parts configured for high-temperature environment use. Thesemethods include densifying precursor structures initially formed byadditive manufacturing (i.e., by 3D printing).

The additive manufacturing methods of embodiments of the disclosure mayuse 3D printers configured to print in true “3D” fashion. That is,conventional additive manufacturing (AM) (e.g., “3D printing”)technologies may be more accurately characterized as “2.5D printing”because conventional AM processes use machines (e.g., “printers”) thatbuild a layer in an x-y plane by disposition of material from a printerhead, stop the printer head, move the build platform or the printer headof the printer in the z-direction, and build another layer in anotherx-y plane. Thus, conventional “3D printing” is a repeated, planarprocess. In contrast, a true “3D” fabrication process may build (e.g.,print) material in more than two axis directions concurrently, i.e.,through the x, y, and z directions concurrently. Conventional AMfabrication systems, by being limited to printing throughout the x-yplane in individual layers, are generally able to print embedded fibersto be aligned in generally only the direction of printing in the x-yplane. Thus, printed fibers are typically not aligned with the directionof the highest-expected stress to be experienced by the printed part inuse. Thus, the limitations of conventional 3D printing techniques andmachines have placed significant limitations on the value of suchcapabilities in forming structures meant to be used under high stress.Embodiments of the present disclosure, however, may allow implementationof true 3D printing, by which fibers can be oriented along any desireddirection or directions, including along a direction of thehighest-expected stress to be experienced by the printed part in use.

Embodiments of the present disclosure may also be conducive for use informing large parts, e.g., integral parts with a greatest dimension ofat least 2 feet (at least 61.0 cm) (e.g., greater than 2.5 feet (76.2cm)). Methods of embodiments of the present disclosure may employrobotic approaches to additive manufacturing that provide greaterflexibility and easier scale-up compared to conventional additivemanufacturing techniques and systems. That is, conventional additivemanufacturing, 3D printing machines often employ a gantry style approachhaving an end-effector (e.g., print head) that lays down the additivematerial in the x-y plane. However, gantry style machine approaches canmake scalability, affordability, and flexibility a challenge forimplementation in association with a single fabrication cell becausethere is a direct correlation between the size of the part beingfabricated and the size of the gantry machine required, where the gantrymachine may be capable of only a single operation at one time. Verylarge parts generally require very large machines, thus driving up therequired footprint and machine cost. Robotic approaches, on the otherhand, may include multiple robots working in association with the samefabrication cell. Additionally, each robot can be mounted to a movablebase that allows for repositioning at different locations within oraround the fabrication cell. Robotic approaches allow for additionalrobot poses that increase the number of degrees of freedom, the abilityto fabricate in 3D, and fabrication flexibility through multiple robotsperforming multiple tasks.

The methods used in embodiments of the present disclosure may formhigh-temperature composite structures that, following densification, areat “near net shape,” meaning that only minor structural refinements maybe required to complete the shaping of the material into the desiredpart. For example, rough edges (if any) may be trimmed, holes may bedrilled, and attachments may be affixed, etc., but without having tosignificantly machine or shape the 3D printed and densified materialinto the desired shape.

Embodiments of the present disclosure may also be conducive for formingstructures with intricate features as integral parts, without the use ofj oints or seals to join what may have been conventionally formed asseveral individual parts. In some embodiments, the methods may be usedto form structures with intentional void space, such as “sandwichstructures.” Sandwich structures generally include two relatively-thin,stiff, and strong faces separated by a relatively thick, lightweightcore defining void space in repeated cells (e.g., honeycomb-shapedcells), separated by struts or walls extending therebetween, e.g., attransverse or acute angles to other structural members. Conventionalprocesses for forming high-temperature composite structures aregenerally not conducive for forming such void-including structuresbecause of the great amount of machining of brittle material that wouldbe required.

Accordingly, disclosed are additive manufacturing methods for forminghigh-temperature composite structures, which composite structures mayexhibit low porosity (e.g., as a result of densification performed afterthe initial additive manufacturing of precursor structures), fibersoriented throughout more than just x- and y-axes, and of potentiallylarge size as unitary, integral pieces, and even integral pieces withcomplex void spaces, such as sandwich structures.

As used herein, the terms “void” and “opening” may mean adistinguishable volume extending into or through a material, or betweenregions of material, leaving an intentional gap in that other materialor between the regions of material. Unless otherwise described, a “void”or an “opening” is not necessarily empty of gaseous or other material.In a final structure, a “void” or “opening” formed in an identifiedmaterial or between regions of an identified material may compriseanother material other than that in which, or between which, the “void”or “opening” was initially defined.

As used herein, the term “high-temperature,” when used in reference toan application (e.g., use) of a structure or to a characteristic of astructure itself—e.g., as in “high-temperature application” and“high-temperature composite structure”—may mean and refer toapplications at, or to a structure configured to withstand withoutdetrimental degradation, temperatures at or exceeding about 2000° F.(1093° C.). As used herein, the term “high-temperature” when referringto a fabrication stage, fabrication process, or fabricationenvironment—e.g., as in a “high-temperature process” or“high-temperature environment” of a fabrication stage—may mean and referto a fabrication stage, fabrication process, or fabrication environmentreaching temperatures of at least about 932° F. (500° C.).

As used herein, the term “at least softened,” in reference to amaterial, means and includes a material that is at least partiallydeformable (e.g., is extrudable), in contrast to a substantially solidmaterial. An “at least softened” material means and includes a“plasticized,” “semi-liquid phase,” and “liquid phase” material.

As used herein, the terms “support material” and “support structure” mayrefer to a material or structure, respectively, that is configured toprovide structural support to another material or structure without thesupport material or support structure being permanently affixed thereto.

As used herein, the terms “z-axis” and “z-direction” mean and refer toan axis or direction, respectively, that is perpendicular to anotherdirection defined as in an “x-y plane.” The “z-axis” or “z-direction”are not necessarily perpendicular to the surface of the earth, unlessthe x-y plane is horizontal to the surface of the earth.

As used herein, the terms “horizontal” or “lateral” mean and include adirection that is parallel to a primary surface of the substrate onwhich the referenced material or structure is located. The “width” and“length” of a respective region or material may be defined as dimensionsin a horizontal plane.

As used herein, the terms “vertical” or “longitudinal” mean and includea direction that is perpendicular to a primary surface of the substrateon which a referenced material or structure is located. The “height” ofa respective region or material may be defined as a dimension in avertical plane.

As used herein, the terms “thickness” or “thinness” mean and include adimension in a straight-line direction that is normal to the closestsurface of an immediately adjacent material or region that is of adifferent composition or that is otherwise distinguishable from thematerial or region whose thickness or thinness is discussed.

As used herein, the term “between” is a spatially relative term used todescribe the relative disposition of one material, region, or componentrelative to at least two other materials, regions, or parts. The term“between” may encompass both a disposition of one material, region, orpart directly adjacent to the other materials, regions, or parts and adisposition of one material, region, or part indirectly adjacent to theother materials, regions, or part.

As used herein, the term “proximate” is a spatially relative term usedto describe disposition of one material, region, or part near to anothermaterial, region, or part. The term “proximate” includes dispositions ofindirectly adjacent to, directly adjacent to, and internal to.

As used herein, the terms “about” and “approximately,” when either isused in reference to a numerical value for a particular parameter, areinclusive of the numerical value and a degree of variance from thenumerical value that one of ordinary skill in the art would understandis within acceptable tolerances for the particular parameter. Forexample, “about” or “approximately,” in reference to a numerical value,may include additional numerical values within a range of from 90.0percent to 110.0 percent of the numerical value, such as within a rangeof from 95.0 percent to 105.0 percent of the numerical value, within arange of from 97.5 percent to 102.5 percent of the numerical value,within a range of from 99.0 percent to 101.0 percent of the numericalvalue, within a range of from 99.5 percent to 100.5 percent of thenumerical value, or within a range of from 99.9 percent to 100.1 percentof the numerical value.

As used herein, the term “substantially,” when referring to a parameter,property, or condition, means and includes the parameter, property, orcondition being equal to or within a degree of variance from a givenvalue such that one of ordinary skill in the art would understand suchgiven value to be acceptably met, such as within acceptablemanufacturing tolerances. By way of example, depending on the particularparameter, property, or condition that is substantially met, theparameter, property, or condition may be “substantially” a given valuewhen the value is at least 90.0% met, at least 95.0% met, at least 99.0%met, at least 99.9% met, or even at least 100% met.

As used herein, reference to an element as being “on” or “over” anotherelement means and includes the element being directly on top of,adjacent to (e.g., laterally adjacent to, vertically adjacent to),underneath, or in direct contact with the other element. It alsoincludes the element being indirectly on top of, adjacent to (e.g.,laterally adjacent to, vertically adjacent to), underneath, or near theother element, with other elements present therebetween. In contrast,when an element is referred to as being “directly on” or “directlyadjacent to” another element, there are no intervening elements present.

As used herein, other spatially relative terms, such as “below,”“lower,” “bottom,” “above,” “upper,” “top,” and the like, may be usedfor ease of description to describe one element's or feature'srelationship to another element(s) or feature(s) as illustrated in thefigures. Unless otherwise specified, the spatially relative terms areintended to encompass different orientations of the materials inaddition to the orientation as depicted in the figures. For example, ifmaterials in the figures are inverted, elements described as “below” or“under” or “on bottom of” other elements or features would then beoriented “above” or “on top of” the other elements or features. Thus,the term “below” may encompass both an orientation of above and below,depending on the context in which the term is used, which will beevident to one of ordinary skill in the art. The materials may beotherwise oriented (rotated ninety degrees, inverted, etc.) and thespatially relative descriptors used herein interpreted accordingly.

As used herein, the terms “comprises,” “comprising,” “includes,” and/or“including” specify the presence of stated features, regions, stages,operations, elements, materials, components, and/or groups, but do notpreclude the presence or addition of one or more other features,regions, stages, operations, elements, materials, components, and/orgroups thereof

As used herein, “and/or” includes any and all combinations of one ormore of the associated listed items.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

As used herein, the terms “configured” and “configuration” mean andrefer to a size, shape, material composition, orientation, andarrangement of a referenced material, structure, assembly, or apparatusso as to facilitate a referenced operation or property of the referencedmaterial, structure, assembly, or apparatus in a predetermined way.

The illustrations presented herein are not meant to be actual views ofany particular material, structure, region, part, component, device,system, or stage of fabrication, but are merely idealizedrepresentations that are employed to describe embodiments of thedisclosure.

The following description provides specific details, such as materialtypes and processing conditions, in order to provide a thoroughdescription of embodiments of the disclosed devices and methods.However, a person of ordinary skill in the art will understand that theembodiments of the devices and methods may be practiced withoutemploying these specific details. Indeed, the embodiments of the devicesand methods may be practiced in conjunction with high-temperaturematerials fabrication techniques employed in the industry.

The fabrication processes described herein do not form a completeprocess flow for fabricating composite materials, structures, parts,components, or assemblies thereof. The remainder of the fabricationprocess flow is known to those of ordinary skill in the art.Accordingly, only the methods and structures necessary to understandembodiments of the present methods are described herein.

Unless the context indicates otherwise, the materials described hereinmay be formed by any suitable technique including. Depending on thespecific material to be formed, the technique for forming, heating(e.g., pyrolyzing, graphitizing, carbonizing, curing), and densifying(e.g., impregnating, depositing, carbonizing, ceramicizing,graphitizing) the material may be selected by a person of ordinary skillin the art.

Reference will now be made to the drawings, where like numerals refer tolike components throughout. The drawings are not necessarily drawn toscale.

Embodiments of the methods for fabricating high-temperature compositestructures may utilize the 3D printing machine and system illustrated inFIGS. 1 through 8 and described below. Other machines, systems, andmethods for 3D printing an initial precursor structure for thefabrication of high-temperature composite structures may utilize themachines, systems, and methods described in any of the following U.S.nonprovisional patent applications, each of which was filed Apr. 10,2019: U.S. patent application Ser. Nos. 16/380,066; 16/380,131;16/380,208; 16/380,272; 16/380,328; and 16/380,390, the disclosure ofeach of which is hereby incorporated herein in its entirety by thisreference. Although a particular fabrication process, e.g., for forminga 3D precursor structure, is disclosed below, it will be appreciatedthat any other suitable fabrication process may be utilized to providethe precursor structure.

Turning to FIG. 1, illustrated is an isometric view of a 3D printingmachine 10 including a robot 12 having a base portion 14, an extensionarm 16 coupled to the base portion 14 by a rotary and pivot joint 18,and a working arm 20 coupled to the extension arm 16 opposite to thebase portion 14 by an elbow pivot joint 22. An end-effector 26 iscoupled to the working arm 20 at an angle opposite to the joint 22 by apivot joint 28 having a coupling mechanism 30. The robot 12 is intendedto represent any suitable positioning device for the end-effector 26.The end-effector 26 operates as a print-head assembly for laying down anat least softened filament (e.g., a thermally softened filament, amolten filament, etc.) for building a complex composite structure asdescribed herein, for example, for laying down an at least softenedfilament that includes a precursor matrix material having, embeddedtherein—at the time of the initial printing—a reinforcing fiber.

The precursor matrix material may be a polymer matrix precursormaterial, which may be formulated to be processed initially as athermoplastic (e.g., during the initial printing of the 3D precursorstructure) and then subsequently as a thermoset (e.g., during subsequentpyrolysis). Such polymer matrix precursor material may comprise, consistessentially of, or consist of a polyetheretherketone (PEEK), apolyetherketoneketone (PEKK), a polyphenylsulfone (PPSF or PPSU), apolyetherimide (PEI), a polyphenylene (PPS), a polyamide (PA), and/or apolyaryletherketone (PAEK). In other embodiments, the precursor matrixmaterial may comprise, consist essentially of, or consist ofacrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and/orpolycarbonate (PC). In still other embodiments, the precursor matrixmaterial may comprise, consist essentially of, or consist of apreceramic material.

The fiber, of the reinforcing fiber, may be a high-temperature materialformulated to withstand the high temperatures to be employed in thepyrolysis and densification processes described further below. In someembodiments, the fibers may comprise, consist essentially of, or consistof fibers selected from the group consisting of carbon fibers, ceramicfibers, glass fibers, quarts fibers, and basalt fibers. Also envisioned,as structural elements (e.g., reinforcing phase materials) of thehigh-temperature composite structures of embodiments of the disclosureare other fibers capable of surviving the pyrolysis and densificationstages (e.g., cycles) of the disclosed methods.

For example, in some embodiments, the precursor matrix material maycomprise a carbon-based precursor matrix material formulated as a PEEKor a PEKK, and the fiber of the fiber reinforcing phase may comprise,consist essentially of, or consist of carbon fibers or ceramic fibers.

The fiber may, in some embodiments, be continuous within the precursormatrix material at the time of the initial 3D printing. In otherembodiments, the fiber may be discrete, long-strand fibers within theprecursor matrix material at the time of the initial 3D printing. Duringthe initial printing, the fiber may be oriented (e.g., aligned) in thedirection of the laid-down material. Therefore, the direction of theend-effector 26 may dictate the orientation of the fibers within theprecursor matrix material.

Various end-effectors will be discussed herein that operate in certainmanners and have certain features, and that can be attached to the robot12. It is noted that during operation, the 3D printing machine 10 may ormay not be positioned within an oven (not shown) so that the temperatureof the printing process and the ambient temperature surrounding the partis controlled.

The end-effector 26 includes an outer housing 34 and a rotatableconnector 36 that is releasably and rotatably connected to the couplingmechanism 30, where the outer housing 34 is shown as being transparentto illustrate the various components therein. Those components include anumber of spools 40, here three, on which a plurality of filaments 42 ofvarious materials (e.g., materials comprising one or more of theaforementioned fibers embedded within one or more of the aforementionedprecursor matrix materials) are wound, a motor 44 for selectively andindependently drawing the filaments 42 off of the spools 40, a rightangle gear box 32 coupled to a filament feed assembly 48 by a shaft 56,a rotary assembly 38 having a barrel 46 that is turned by an indexingmotor 58 and through which the filaments 42 are drawn and melted, an endplate 54 mounted to an end of the barrel 46 and a nozzle assembly 50that extends through the end plate 54 and is part of the extrudermodule. The spools 40 can be mounted in the end-effector 26 as shown, ormounted remotely with the material being fed to the end-effector 26through a tube (not shown). Alternately, the stock material can beprovided by pellets instead of using the filament 42.

FIG. 2 is an isometric view of a continuous fiber extruder module 140that is one non-limiting example of the type of extruder module that canbe provided within the end-effector 26 and is rotated by the rotaryassembly 38, where the module 140 is fitted with a mounting bracket 142that allows it to be attached to the end-effector 26. The module 140receives a filament 138 (see FIG. 4) (e.g., the filament 138 comprisingat least one of the aforementioned fibers embedded in at least one ofthe aforementioned precursor matrix materials) through a filament guidetube 144, where the filament 138 passes through a filament guide tubemounting bracket 146 and then between a feed roller 148 and a clamproller 150. The feed roller 148 is coupled to a feed motor 152 having apower connector 154 and an encoder 156, which provides the motive forceto feed the filament 138 through the module 140. The clamp roller 150 iscoupled to a clamp roller actuator 158 that presses the clamp roller 150against the filament 138, thus pinching the filament between the feedroller 148 and the clamp roller 150 with a selected amount of force,which ensures that sufficient traction is created between the feedroller 148 and the filament 138 to allow the filament 138 to be fedwithout slipping.

The filament 138 then passes through a filament guide 184 and into anozzle assembly 162. FIG. 3 is an isometric view and FIG. 4 is across-sectional view of the nozzle assembly 162 separated from themodule 140. The nozzle assembly 162 includes a filament inlet 164 and anozzle 166, around which are clamped a cooling block 168 and a heatingblock 170, where the cooling block 168 receives a liquid coolant througha set of coolant hose connectors 172. The heating block 170 is heated bya heating element 174 and its temperature is monitored by a temperaturesensor 176, which could be a thermocouple, thermistor, resistancetemperature detector (RTD), or similar type of temperature sensor. Thisarrangement ensures that the filament 138 remains at a temperature thatis less than the melting point of its polymer component (or otherprecursor matrix material) until it arrives at a nozzle tip 180 of thenozzle 166. The filament 138 is then heated at the end of the nozzle 166to melt the polymer (or other precursor matrix material) so that thefilament 138 will bond to a build surface 190 when it emerges from thenozzle tip 180.

A cutter 182 is provided between a filament guide 184 and the nozzleassembly 162 that is moved by a cutter actuator 186 and is constrainedby a cutter guide 188. When the cutter actuator 186 is actuated, itmoves the cutter 182 towards the filament 138 at high speed and with aselected amount of force, in a direction perpendicular to the filamentfeed direction, shearing the filament 138 (e.g., and the reinforcingfiber within the precursor material) against the underside of thefilament guide 184 and cutting through the entire filament 138 (e.g.,including the fiber within the precursor matrix material). This allowsthe filament 138 to be automatically cut to the appropriate length as itis being printed. The filament 138 is only extruded from the nozzle 166in one direction, so the nozzle 166 must be rotated to differentorientations in order to be able to extrude the filament 138 indifferent directions and to orient the fiber (e.g., within the precursormatrix material) of the filament 138 in a desired direction. The desireddirection need not be restricted to only an x-y plane, however. This isdifferent from conventional 3D printing nozzle designs, which are notsensitive to the rotation of the nozzle 166 and can print in anydirection as long as the print direction is normal to the axis of thenozzle 166, i.e., typically any direction within the x-y plane for atypically vertically downward directed 3D printing nozzle.

The continuous fiber-reinforced 3D printing process is sensitive to theorientation of the nozzle assembly 50. The machine overcomes some ofthis sensitivity by making the nozzle assembly 50 rotatable.Additionally, by making the nozzle assembly 50 rotatable relative to therest of the end-effector 26, the direction of the filament 42 as it isextruded from the end-effector 26 can be controlled without needing torotate the entire end-effector 26. The end-effector 26 may be relativelylarge and unwieldy compared to the rotary assembly 38, so being able tocontrol the orientation of the extruder module independently of theorientation of the end-effector 26 significantly improves dexterity ofthe 3D printing machine 10.

As mentioned above, the part (e.g., a high-temperature compositestructure) that is being built by the printing process may be formed ona build platform. In the design of the 3D printing machine 10 a rotarycircular table 70 may be employed on which a part 72 (e.g., ahigh-temperature composite structure) being printed or fabricated isshown. An optional riser 74 is provided at a center of the table 70 andthe part 72 is positioned on the riser 74. However, it is noted that insome designs, the riser 74 may not be needed. The end-effector 26 isshown positioned adjacent to the part 72 and is in the horizontalorientation. By providing the riser 74 on which the part 72 sits, thepart 72 is separated some suitable distance from a top surface 76 of thetable 70 so as to provide clearance between the end-effector 26 and thetable 70 that is desirable for effectively printing small-diameterparts. In one embodiment, the riser 74 is fabricated from a highlythermally conductive material, such as copper, so as to improve thermaltransfer to the part 72 and maintain part thermal stability and adhesionof the part 72 to the surface of the riser 74. The riser 74 can beprovided in different shapes, sizes and heights to be more effective forfabrication of parts having a wide range of geometries. A side of thetable 70 is shown as being transparent to illustrate suitable components78 therein that allow the table 70 to be rotated and allow the riser 74to be heated.

FIG. 5 is a top view of a part 90 (e.g., a high-temperature compositestructure) being fabricated by a robotic placement process on a buildplate (not shown), such as by the 3D printing machine 10 shown inFIG. 1. As discussed above, the robotic placement process may depositrows of adjacent filaments 92 to form layers 94 that are stacked on topof each other to form the part 90. Known 3D fabrication processessequentially deposit each filament 92 directly adjacent to thepreviously deposited filament 92. There are required tolerances of thepositional accuracy of the filaments 92 as they are being deposited,i.e., how far off the position of the filaments 92 can be from a desiredlocation. These tolerances, if directionally similar, tend to accumulateas the filaments 92 are being deposited for a particular layer, whichcan create a slight overlap of the filaments 92. This overlapping of thefilaments 92 when deposited sequentially can, in turn, cause positionalerrors to accumulate and cascade through a layer. Eventually, if enoughoverlap has accumulated, there is no longer enough room on the layer 94in the desired location to deposit the next filament 92. As will bediscussed below, according to this embodiment of the disclosure, thepart 90 is fabricated by non-sequentially depositing the filaments 92for each part layer 94. By providing non-sequential depositing of thefilaments 92, the tolerances tend to average out and tend not to buildup on each other.

As illustrated in this embodiment, a first set of odd-numbered filaments96 are deposited for a certain one of the layers 94, which defines rowsof gaps between adjacent filaments 96 that are about one filament widthapart. The fabrication process then deposits a second set ofeven-numbered filaments 98, shown as being shaded merely forillustration purposes, in the gaps between the filaments 96, where thefirst set of odd-numbered filaments 92 have already begun to harden,which better defines the gap therebetween. The first set of filaments 96is referred to as odd-numbered filaments because the first depositedfilament in the first set is deposited in row number one, the seconddeposited filament is deposited in row number three, etc. The second setof filaments 98 is referred to as even-numbered filaments because thefirst deposited filament in the second set is deposited in row numbertwo, the second deposited filament is deposited in row number four, etc.Thus, instead of depositing the filaments 92 sequentially, where onefilament 92 is deposited directly adjacent to the filament 92 that waspreviously deposited as was done in the prior art, this embodimentdeposits the filaments 92 non-sequentially and in spaced relationship sothat every other filament 92 is first deposited, and then filaments 92are deposited in the gaps therebetween. It is noted that although thisembodiment deposits the filaments non-sequentially by first depositingthe odd-number of rows and then depositing the even-numbered rows, thisis merely an example. Other embodiments could deposit the filamentsnon-sequentially in any suitable manner as long as gaps are providedbetween each set of filaments that are deposited at a particular time.This process provides a number of advantages including improving thereliability of the fabrication process, reducing the sensitivity of theprocess to fly height and variations in feedstock material lineardensity, a higher percentage fill, reduction in part porosity and anincrease in part fiber volume.

The filaments 92 can be formed of any material suitable for the purposesdiscussed herein, such as the various thermoplastics and polymers (orother precursor matrix materials) mentioned above. In one non-limitingembodiment, the filaments 92 comprise, consist essentially of, orconsist of continuous fiber filaments, such as continuous carbon fiber(CCF) filaments—which tend to be of higher strength that is desired forcertain products—where each filament 92 has many continuous fibers thatextend from one end of the filament 92 to the other end of the filament92 and are encapsulated in a suitable polymer (e.g., one or more of theaforementioned precursor matrix materials) to provide the desiredstrength. Other suitable continuous fiber filaments may comprise,consist essentially of, or consist of any one or more of theaforementioned fiber materials. Additionally, any of these fibers can bechopped or sectioned so that they are not continuous from one end of thefilament 92 to the other end of the filament 92, and are also enclosedwithin a suitable polymer (e.g., such as one of the aforementionedpolymer precursor matrix materials) (or another one or more of theaforementioned precursor matrix materials), which tend to be of a lowerstrength than continuous fiber filaments. Typical widths of thefilaments 92 are in the range of 3.5 mm to 7 mm and a typical thicknessof the filaments 92 can be 0.25 mm to 0.5 mm.

FIG. 6 is a side view of a part assembly 100 (e.g., a high-temperaturecomposite structure) fabricated by a robotic placement process, such asby the 3D printing machine 10 shown in FIG. 1. The part assembly 100includes a support structure 102 fabricated on a build-plate 104 and apart 106 fabricated on the support structure 102. The support structure102 may be fabricated by the same robotic placement process as the part106, and may be formed of, for example, layers of pure polymer (or otherprecursor matrix material) filaments or of polymer (or other precursormatrix material) filaments including chopped or discontinuous fibers ofthe type discussed above, e.g., for FFF. In some embodiments, toincrease the adhesion between the desired part layers, a roboticplacement process may fabricate the part layers in an alternatingsequence of first layers 108 including filaments made of a desiredmaterial for the final part and second layers 110 including filamentsmade of a desired material to increase or enhance the adhesion betweenthe layers 108 without significantly reducing the structural integrityof the final part. The filaments of one material may be provided, forexample, by a first extruder module in the extruder module 60, and thefilaments of the other material may be provided by a second extrudermodule in the extruder module 60. In one non-limiting embodiment, thefirst layers 108 may include continuous fiber filaments and the secondlayers 110 may include pure polymer (or other precursor matrix material)filaments or polymer (or other precursor matrix material) filaments withdiscontinuous fibers. However, it is noted that this is merely forillustrative purposes in that the first layers 108 may be, generally,strength layers while the second layers 110 may be, generally, adhesionlayers, which may be other materials than described above.

The thickness of the second layers 110 may be minimized to the extentpossible, such as 0.13 mm, or about half of the thickness of the firstlayers 108. Each layer 108 and 110 may be deposited in any suitableorientation relative to the other layers 108 and 110, such as 0°, 45°,90°, 135°, etc. This robotic placement process provides a number ofadvantages including improved reliability of the robotic placementprocess, improved robotic placement process speed because the secondlayers 110 can be deposited more quickly than the first layers 108,improved inter-layer adhesion, and a reduction in the permeability ofthe finished part.

FIG. 7 is a side view of a fabrication assembly 120 including a toolingor support structure 122 that has been fabricated by an FFF process,such as by the 3D printing machine 10 shown in FIG. 1, on a build-plate124, as discussed above. A part (not shown) will be fabricated on thesupport structure 122 opposite to the build-plate 124. An FFF depositionnozzle 126 is shown relative to the support structure 122 and isintended to represent the nozzle that fabricated the support structure122, which would have a certain configuration for that purpose. Thefabrication process of the support structure 122 would be such thatsurface imperfections, shown here as steps 128, would form between theseparate layers in the support structure 122. The steps 128 reduce theaccuracy of depositing the part (not shown) thereon and reduce theability to remove the part from the support structure 122 withoutdamaging it because the polymer material of the part gets into and issecured within various nooks and crannies within the support structure122.

FIG. 8 is a side view of the fabrication assembly 120 showing thesupport structure 122 on the build-plate 124. According to thisembodiment, prior to the part being fabricated on the support structure122, a nozzle 130 that is used to deposit the filaments for the part maybe first heated and then used to smooth out the steps 128 to form asmoothed surface 132 on the support structure 122. The nozzle 130 may beconfigured to have an indented (e.g., chamfered) or rounded corner 134that allows the nozzle 130 to more easily provide the desired smoothingaffect. In an alternate embodiment, a dedicated ironing tool (not shown)may be used instead of the nozzle 130 to smooth out the surface of thesupport structure 122. As above, the various filaments for the supportstructure 122 and the part can be formed of any material suitable forthe purposes discussed herein, such as the various thermoplastics andpolymers (or other precursor matrix materials) mentioned above. Thefilaments may include continuous fiber filaments or filaments havingfibers that are chopped or sectioned so that they are not continuousfrom one end of the filament to the other end of the filament, and arealso enclosed within a suitable polymer (or other precursor matrixmaterial). This process provides a number of advantages includingimproved reliability of the robotic placement process and improvedfinish of the part surface after the support structure 122 is removed.

Accordingly, using the system of FIGS. 1 through 8, for example, aprecursor structure—comprising a fiber reinforcing phase embedded withina precursor matrix material—is formed by a manufacturing process, suchas, for example, additive manufacturing (e.g., 3D printing) in a mannerthat may direct printing along even directions that are not strictlywithin an x-y plane for each respective printed strata of a structure.Therefore, the fibers within the precursor structure may be oriented inany desired direction, including in a direction aligned with a directionof a greatest expected stress to be experienced by the part to befabricated.

As noted above, in some embodiments, the precursor structure may beprovided through other mechanized processes and/or methods.

With reference to FIG. 9, charted are various embodiments for continuingthe fabrication of composite structures (e.g., high-temperaturecomposite structures) subsequent to the formation of the initial 3Dprecursor structure, e.g., after the rigidized preform manufacture 901of the methods of FIG. 9. The method may continue by subjecting the 3Dprinted precursor structure to thermal processing (e.g., pyrolysis andheat treatment (stage 902)). During this process, the precursorstructure may be exposed to temperatures exceeding about 932° F. (500°C.) (e.g., in one or more high-temperature fabrication stages), duringwhich the precursor matrix material pyrolyzes, and inorganics from theprecursor matrix material (if any) outgas, leaving the fibers within aremnant of solidified carbon matrix material. This post-pyrolysis,intermediate structure will be porous and therefore unsuitable for usein high-temperature environments, such as in aerospace flights.Therefore, the method continues by subjecting the post-pyrolysis,intermediate structure to densification processes (e.g., stages orcycles 910 or 920 of FIG. 9).

In embodiments configured to form high-temperature composite structurescomprising carbon-carbon composite materials, the post-pyrolysis,intermediate structure may be densified using a carbon-carbondensification cycle 910. The post-pyrolysis, intermediate structure maybe impregnated with a carbon precursor 911 and heated (e.g., in an oven,furnace, autoclave, or other high-temperature environment, e.g., at atemperature exceeding about 932° F. (500° C.), e.g., up to a temperatureof about 5432° F. (3000° C.)) to carbonize 912 and graphitize 913 theimpregnated structure (e.g., separately or concurrently), to add solidcarbon material into the pores of the post-pyrolysis, intermediatestructure. Various techniques for impregnating porous structures withcarbon precursor, e.g., for carbonizing and/or for graphitizing, aregenerally known in the art and so are not described in detail herein.Therefore, some embodiments of the disclosure may impregnate thestructure with carbon using, e.g., melt infiltration, chemical vapordeposition (CVD), or other similar material-infusion processes. However,in some embodiments of the disclosure, the post-pyrolysis, intermediatestructure may be impregnated with the carbon precursor (e.g., in stage911) in the form of a liquid resin (e.g., a liquid organic resin). Insome embodiments in which the precursor matrix material comprised acarbon precursor material, the carbon precursor (e.g., the liquidorganic resin) for stage 911 may have the same formula as the precursormatrix material, though with a lower viscosity. The liquid organic resinmay be a low-viscosity, liquid organic resin. As used herein“low-viscosity” may mean and refer to a viscosity not exceeding about 50seconds, when measured using the Saybolt Furol method (ASTM E102). Insome embodiments, the viscosity of the liquid resin (e.g., the liquidorganic resin; e.g., the low-viscosity, liquid organic resin) may betailored to be low enough to enable the liquid to enter pores of thepost-pyrolysis, intermediate structure and high enough to enable carbonof the liquid organic resin to deposit on already-solidified carbonmaterial during the subsequent carbonization 912 and graphitization 913stages.

Stages 911, 912, and 913 may, optionally, be repeated (as indicated bystage 914), as desired, until the now-rigid, high-temperature compositestructure (e.g., in this embodiment, a high-temperature carbon-carboncomposite structure) exhibits a desired density. The resulting structurewill be substantially non-porous (e.g., less porous than that followingthe pyrolysis and heat treatment stage 902) and conducive for use inhigh-temperature environments.

In embodiments to form the high-temperature composite structure as aceramic matrix composite (CMC) structure, following the pyrolysis andheat treatment of stage 902, the post-pyrolysis, intermediate structuremay be densified by a CMC densification cycle 920, which includesimpregnating the post-pyrolysis, intermediate structure with apreceramic polymer precursor material 921. As above, the impregnationmay be carried out using material-infusion methods such as meltinfiltration, chemical vapor deposition (CVD), or other similarmaterial-infusion methods. In other embodiments, impregnating thepost-pyrolysis, intermediate structure with a preceramic polymerprecursor material 921 may use a liquid resin. For example, inembodiments in which the precursor matrix material for the 3D printingprocess was a preceramic polymer precursor material, the preceramicpolymer precursor material of stage 921 may have a formula the same asthe precursor matrix material for the 3D printing process, though—in atleast some embodiments—with a lower viscosity. Therefore, in someembodiments, the preceramic polymer precursor material of stage 921 may,like the carbon precursor of stage 911, be a low-viscosity, liquidresin. Heating the impregnated structure (e.g., in an oven, furnace,autoclave, or other high-temperature environment, e.g., at a temperatureexceeding about 932° F. (500° C.), e.g., up to a temperature of about3000° F. (1649° C.)), subjects the impregnated structure to pyrolysis922 and heat treatment 923 to solidify the ceramic material within thepreceramic polymer precursor material. Stages 921, 922, and 923 may,optionally, be repeated (as indicated by stage 924) one or more timesuntil the now-rigid, high-temperature composite structure (e.g., in thisembodiment, a high-temperature CMC structure) exhibits a desireddensity. The resulting structure will be substantially non-porous (e.g.,less porous than that following the pyrolysis and heat treatment stage902) and conducive for use in high-temperature environments.

In some embodiments, both the carbon-carbon densification cycle(s) 910and the CMC densification cycle(s) 920 may be used in the method offabricating the high-temperature composite structure. For example, afterpyrolysis and heat treatment (stage 902), the post-pyrolysis,intermediate structure may be subjected to the carbon-carbondensification cycle 910 one or more times and then subjected to the CMCdensification cycle 920 one or more times, vice versa, and/or the cyclesmay be alternated. As another example, after pyrolysis and heattreatment (stage 902), the post-pyrolysis, intermediate structure may besubjected to one or more of the carbon-carbon densification cycles 910or one or more of the CMC densification cycles 920, then to one or moreof the other of the cycles 910, 920, before being subjected again to theoriginal one of the cycles 910, 920. So, the method may include only thecarbon-carbon densification cycles 910 one or multiple (e.g., two toten, or more) times, only the CMC densification cycles 920 one ormultiple (e.g., two to ten, or more) times, or some combination of thetwo cycles 910, 920 in any order.

After the densification cycle(s) 910, 920 the now-rigid, densified,nonporous structure may then be subject to final processing (e.g., finalmachining 930) to complete the fabrication of the structure, though itis expected that the final machining 930 may be relatively minortrimming, drilling of holes, etc., compared to conventional fabricationprocesses. In other words, the final machining 930 may not includeaddition of seals, attachments of joints, or complex assembly of severalsmaller parts because the methods disclosed herein enable formation ofintegral part, even large, intricate parts.

Because the 3D printing (i.e., the rigidized preform manufacture 901)process used in the embodiments of the disclosure enable true 3Dprinting (e.g., using the machine and system of FIGS. 1 through 8), andenable forming even intricate structures with void space without havingto extensively post-shape the structure, complex and large parts may beformed as unitary, integral pieces, e.g., without the extensive cost andtime that would normally be required for complicated molds orpost-processing machining.

For example, FIG. 10 illustrates a high-temperature composite structure1000 that may be formed using any of the embodiments and materialsdescribed above. The high-temperature composite structure 1000 may be asandwich structure, with a pair of at least partially planar andcontinuous portions (e.g., surfaces) (e.g., an upper portion 1002, alower portion 1004) between which is an intermediate portion 1005defining a series of cells 1006 of void space. Notably, by the methodsof the disclosure, the upper portion 1002, the intermediate portion1005, and the lower portion 1004 may all be integrally formed within oneanother. For example, using the machine and system of FIG. 1 (or othersuitable formation process) and the aforementioned precursor matrixmaterial with embedded fiber material as the filament 42 used in themachine of FIG. 1, and defining a horizontal plane (e.g., horizontal tothe surface of the earth, normal to the direction of gravity) asdefining an x-y plane (as indicated in the axis guide of FIG. 10), thehigh-temperature composite structure 1000 of FIG. 10 may be formed inthe y-axis direction, from rear 1008 to front 1009 in successiveindividual or coiled layers building the high-temperature compositestructure 1000 in the horizontal direction (e.g., because the machine ofFIG. 1 enables other than mere x-y then z-axis orientations of layingdown the filament 42). The 3D printed, precursor structure may then besubjected to the remaining stages of the method(s) of FIG. 9 to form thecompleted, high-temperature, composite structure 1000 of FIG. 10.

Structures formed by the methods of the present disclosure may beconfigured for use in a variety of structures, e.g., aerospacestructures (e.g., vehicles or components thereof (e.g., rocket nozzles,thermal protection systems (TPS), inlets, isolators, antenna windows)),aeronautical structures (e.g., jet engine components), high-speedstructures (e.g., vehicles or components thereof (e.g., vehiclesconfigured to travel at speeds of at least, e.g., Mach 5)), nuclearreactor shielding, internal combustion engine components (e.g.,cylinders, pistons, engine blocks), etc.

Structures formed by the methods herein may also be configured andconducive for use in environments with significant fluctuations intemperatures. For example, the composite materials of the resultinghigh-temperature composite structures may exhibit negligible or lowcoefficients of thermal expansion (CTE). Therefore, if subjected toenvironments passing through great differences in temperature (e.g.,orbiting in space with 200°+ temperature differentials), the structureof the high-temperature composite structures may retain their fabricatedstructure (e.g., optical bench structures), rather than warping anddistorting in shape.

While the disclosed methods, stages, materials, structures, apparatus,and systems are susceptible to various modifications and alternativeforms in implementation thereof, specific embodiments have been shown byway of example in the drawings and have been described in detail herein.However, the disclosure is not intended to be limited to the particularforms disclosed. Rather, the disclosure encompasses all modifications,combinations, equivalents, variations, and alternatives falling withinthe scope of the disclosure as defined by the following appended claimsand their legal equivalents.

1. A method for forming a high-temperature composite structure, themethod comprising: forming a 3D precursor structure, comprising:depositing, along a direction, an amount of a filament material, thefilament material comprising a precursor matrix material having embeddedtherein a fiber material; depositing an additional amount of thefilament material on the amount of the filament material; pyrolyzing the3D precursor structure to form a pyrolyzed intermediate structure;impregnating the pyrolyzed intermediate structure with a liquid resin toform an impregnated structure; and exposing the impregnated structure toa high-temperature environment to solidify material from the liquidresin within pores of the pyrolyzed intermediate structure.
 2. Themethod of claim 1, further comprising selecting the precursor matrixmaterial from the group consisting of a polyetheretherketone (PEEK), apolyetherketoneketone (PEKK), a polyphenylsulfone (PPSF or PPSU), apolyetherimide (PEI), a polyphenylene (PPS), a polyamide (PA), and apolyaryletherketone (PAEK).
 3. The method of claim 1, further comprisingselecting the fiber material from the group consisting of carbon fibers,ceramic fibers, glass fibers, quartz fibers, and basalt fibers.
 4. Themethod of claim 1, further comprising: selecting the precursor matrixmaterial from a PEEK and a PEKK; and selecting the fiber material fromcarbon fibers and ceramic fibers.
 5. The method of claim 1, whereindepositing, along the direction, the amount of the filament materialcomprises depositing the amount of the filament material along adirection not within a horizontal plane.
 6. The method of claim 1,wherein forming the 3D precursor structure comprises integrally formingan intermediate portion defining a series of void space cells between anupper portion and a lower portion of the 3D precursor structure.
 7. Themethod of claim 1, wherein impregnating the pyrolyzed intermediatestructure with the liquid resin comprises impregnating the pyrolyzedintermediate structure with a low-viscosity carbon precursor material.8. The method of claim 1, wherein impregnating the pyrolyzedintermediate structure with the liquid resin comprises impregnating thepyrolyzed intermediate structure with a liquid preceramic polymerprecursor material.
 9. The method of claim 1, further comprising, afterthe exposing of the impregnated structure to the high-temperatureenvironment, repeating the impregnating and the exposing at least once.10. The method of claim 9, wherein repeating the impregnating and theexposing at least once comprises repeating the impregnating and theexposing at least once with a different liquid resin than in the initialimpregnating of the pyrolyzed intermediate structure.
 11. The method ofclaim 1, wherein forming a 3D precursor structure comprises forming the3D precursor structure to define at least one void space.
 12. The methodof claim 1, wherein forming a 3D precursor structure comprises formingthe 3D precursor structure as a unitary, integral structure defining agreatest dimension of at least 61.0 cm.
 13. A method for forming acomposite structure, the method comprising: heating a precursorstructure comprising a precursor matrix material embedded with areinforcing material to solidify at least some of the precursor matrixmaterial and form an intermediate structure; impregnating theintermediate structure with a liquid resin to add carbon or ceramicmaterial to the intermediate structure and form a densified structure;and heating the densified structure at a temperature between about 932°F. (500° C.) and about 5432° F. (3000° C.).
 14. The method of claim 13,further comprising, before heating the precursor structure, forming theprecursor structure, comprising three-dimensional printing a precursormatrix material embedded with a reinforcing material.
 15. The method ofclaim 14, wherein three-dimensional printing the precursor matrixmaterial comprises orienting the reinforcing material along anon-horizontal axis.
 16. The method of claim 14, whereinthree-dimensional printing the precursor matrix material embedded withthe reinforcing material comprises three-dimensional printing theprecursor matrix material embedded with a continuous fiber material. 17.The method of claim 14, wherein three-dimensional printing the precursormatrix material embedded with the reinforcing material comprisesthree-dimensional printing the precursor matrix material embedded withdiscrete strands of a fiber material.
 18. The method of claim 13,further comprising repeating the impregnating and the heating at leastone additional time.
 19. A method of forming a high-temperaturecarbon-carbon or ceramic matrix composite sandwich structure, methodcomprising: operating a robotic 3D printing machine to lay, along anaxis, a precursor matrix material comprising a fiber embedded thereinand form a 3D precursor structure defining at least one void betweenplanar portions; pyrolyzing the 3D precursor structure at a temperatureexceeding about 932° F. (500° C.) to form a porous intermediatestructure; introducing, into pores of the porous intermediate structure,a liquid resin comprising carbon or a preceramic material to form animpregnated intermediate structure; and exposing the impregnatedintermediate structure to a temperature exceeding about 932° F. (500°C.).
 20. The method of claim 19, not comprising use of a prefabricatedmold.
 21. The method of claim 19, wherein operating the robotic 3Dprinting machine to lay, along the axis, the precursor matrix materialcomprises directing a nozzle of the robotic 3D printing machine along ahorizontal direction.
 22. The method of claim 19, wherein: pyrolyzingthe 3D precursor structure at the temperature exceeding about 932° F.(500° C.) comprises pyrolyzing the 3D precursor structure at atemperature exceeding about the 932° F. (500° C.), up to about 5432° F.(3000° C.); and exposing the impregnated intermediate structure to thetemperature exceeding about 932° F. (500° C.) comprises exposing theimpregnated intermediate structure to the temperature exceeding aboutthe 932° F. (500° C.), up to about 5432° F. (3000° C.).
 23. A compositestructure, formed by pyrolyzing and densifying a 3D printed precursorstructure of a precursor matrix material embedded with a reinforcingphase, the composite structure comprising: an intermediate portion,defining a series of cells, between an upper portion and a lowerportion, the intermediate portion, the upper portion, and the lowerportion each comprising a composite material comprising the reinforcingphase embedded within a matrix phase formed from the precursor matrixmaterial, the intermediate portion, the upper portion, and the lowerportion being integral with one another.
 24. The composite structure ofclaim 23, wherein the matrix phase comprises a carbon-based material.25. The composite structure of claim 23, wherein the matrix phasecomprises a ceramic material.
 26. The composite structure of claim 23,wherein the upper portion and the lower portion define at leastpartially planar, continuous surfaces.
 27. The composite structure ofclaim 23, wherein the composite structure comprises at least a portionof a structure of a rocket nozzle, a thermal protection system (TPS), ora vehicle configured to travel at speeds of at least Mach
 5. 28. Ahigh-temperature composite structure, comprising: a pyrolyzed structurecomprising a matrix phase having an embedded reinforcing phase, thepyrolyzed structure defining a sandwich structure; and solid carbon orceramic material filling pores of the pyrolyzed structure.